Lipids have multiple industrial applications, including applications in the cosmetic and food industries, as well as serving as precursors for biodiesel and various biochemicals. Microbial lipids are produced by many oleaginous organisms, including the yeast Y. lipolytica (Beopoulos A, et al. Y. lipolytica as a model for bio-oil production. Prog Lipid Res. 2009 November; 48(6):375-87). Lipid yield in oleaginous organisms can be increased by up-regulating and/or down-regulating or deleting genes implicated in the lipid pathway (Tai M. et al. Engineering the push and pull of lipid biosynthesis in oleaginous yeast Y. lipolytica for biofuel production. Metab Eng. 2013 January; 15:1-9; Beopoulos A, et al. Control of lipid accumulation in the yeast Y. lipolytica. Appl Environ Microbiol. 2008 December; 74(24): 7779-7789). For example, it was reported that up-regulation of native Y. lipolytica DGA1 significantly increased lipid yield and productivity (Tai M, et al. Metab Eng. 2013 January; 15:1-9). DGA1 (diacylglycerol acyltransferase) is one of the key components of the lipid pathway involved in the final step of synthesis of triacylglycerol (TAG), which is a major component of lipids (Beopoulos A, et al. Identification and characterization of DGA2, an acyltransferase of the DGAT1 acyl-CoA:diacylglycerol acyltransferase family in the olcaginous yeast Y. lipolytica. New insights into the storage lipid metabolism of oleaginous yeasts. Appl Microbiol Biotechnol. 2012 February; 93(4):1523-37). The Tai 2013 publication disclosed data suggesting that DGA1 efficiency may be a significant factor that is critical for high level of lipid accumulation in oleaginous organisms. Besides manipulation of homologous genes, heterologous genes also may be introduced into the host genome and have significant effect on lipid production and composition (Courchesne N M, et al. Enhancement of lipid production using biochemical, genetic and transcription factor engineering approaches. J Biotechnol. 2009 Apr. 20 141(1-2):31-41). Further, other oleaginous yeast, such as R. toruloides and L. starkeyi, are able to accumulate significantly more lipids compared to the wild-type Y. lipolytica strains (Sitepu I R, et al. Manipulation of culture conditions alters lipid content and fatty acid profiles of a wide variety of known and new oleaginous yeast species. Bioresour Technol. 2013 September; 144:360-9; Liang M H, et al. Advancing oleaginous microorganisms to produce lipid via metabolic engineering technology. Prog Lipid Res. 2013 October; 52(4):395-408; Ageitos J M, et al. Oily yeasts as oleaginous cell factories. Appl Microbiol Biotechnol. 2011 May; 90(4):1219-27; Papanikolaou S, et al. Lipids of oleaginous yeasts. Part I: Biochemistry of single cell oil production. European Journal of Lipid Science and Technology 2011 June; 113(8): 1031-1051; Pan L X, et al. Isolation of Oleaginous Yeasts, Food Technol. Biotechnol. 2009 47(2):215-220; Ratledge C. et al. The biochemistry and molecular biology of lipid accumulation in oleaginous microorganisms. Adv Appl Microbiol. 2002 51:1-51; Kaneko H. et al. Lipid composition of 30 species of yeast. Lipids. 1976 December; 11(12):837-44). Despite efforts to increase lipid yield in Y. lipolytica by overexpression of heterologous DGA1 from Mortierella alpine, no significant effect on lipid production levels has been reported (U.S. Pat. No. 7,198,937).
Remarkably, Applicants have solved the long-standing problem by overexpressing polynucleotides encoding DGA1 from highly olcaginous organisms. These polynucleotides, when introduced in yeast, such as Y. lipolytica, created engineered yeast strains capable of increased yields of lipids compared to strains overexpressing native Y. lipolytica DGA1.